In recent years, various proposals have been made in regard to automotive vehicle body structures to maximize the protection of vehicle occupants at the time of a vehicle crash. For instance, proposals have been made to minimize the deceleration of the part of the vehicle body occupied by vehicle occupants by properly selecting the deformation of the remaining part of the vehicle body, and preventing the former part of the vehicle body from deforming (see Japanese patent laid open publication No. 7-101354, for instance).
When a vehicle occupant is restrained to the seat by a seat belt, the forward inertial force acting upon the vehicle occupant at the time of a vehicle crash starts rising only after the vehicle occupant is fully restrained by the seat belt. Because the seat belt inevitably has a certain resiliency, the deceleration acting on the vehicle occupant reaches a maximum level when the vehicle occupant is thrown forward, and the maximum elongation of the seat belt has occurred. The maximum level is higher as the forward movement of the vehicle occupant under the inertial force increases, and is known to substantially exceed the average deceleration of the vehicle body. Therefore, to minimize the impact which the vehicle occupant receives at the time of a vehicle crash, it is necessary to adjust the time history of the vehicle body deceleration so as to minimize the time delay in the rise in the deceleration of the vehicle occupant with respect to the deceleration of the vehicle body.
Accordingly, by conducting simulations, the inventors have discovered that, for a given deformation stroke of the vehicle body for absorbing the impact of a vehicle crash, the peak value of the deceleration of the vehicle occupant is smaller when the vehicle body deceleration is initially allowed to rise sharply and then gradually reduced to a constant value than when the vehicle body deceleration is kept constant from the early stage of the crash or allowed to rise only gradually.